1. Field of the Invention
This invention is generally directed to semiconductor devices, and, more particularly high performance semiconductor device.
2. Description of the Related Art
Generally speaking, there is a constant drive in the semiconductor industry to make semiconductor devices, i.e., transistors, smaller and smaller. All other things being equal, semiconductor devices with smaller feature sizes tend to be more efficient, i.e., faster, and may be more cost-effective to manufacture in that a greater number of devices can be fabricated on a single wafer.
This constant drive to reduce the feature size of semiconductor devices has resulted in a corresponding scaling of many of the components of a semiconductor device. For example, as the gate length of semiconductor devices decreases, the thickness of the gate dielectric layer, i.e., the gate oxide layer, which has traditionally been made of silicon dioxide, also decreases. However, the reduction in the thickness of traditional silicon dioxide gate dielectric layers has resulted in several problems. For example, when silicon dioxide gate dielectric layers approach a thickness of approximately 20 .ANG., leakage of current from the conductor to the channel may increase. Additionally, it is difficult to fabricate silicon dioxide gate dielectric layers having a thickness of approximately 20 .ANG. or less with the requisite quality required for gate dielectric layers.
Another problem may arise when a relatively thin silicon dioxide gate dielectric layer is used in a PMOS device. The gate electrode in PMOS devices is generally a doped polysilicon. Such doping is typically accomplished by the addition of boron to the polysilicon gate electrode layer. However, thin silicon dioxide gate dielectric layers, e.g., those having a thickness of approximately 20 .ANG. or less, may not provide a sufficient barrier to prevent the migration of free boron atoms into the semiconductor substrate.
On the other hand, traditional gate oxide layers cannot be made too thick without adversely affecting the performance of the semiconductor devices. As is well known to those skilled in the art, the thickness of traditional gate oxide layers is tightly controlled to assure that the gate oxide layer is thin enough that an appropriate current can be induced in the gate region of a device by applying the appropriate voltage to a conductor above the gate oxide layer. Thus, as the feature size of semiconductor devices continues to decrease, there is a need to produce semiconductor devices having a gate dielectric layer that is dielectrically equivalent to a silicon dioxide gate layer having a thickness below approximately 20 .ANG..
The present invention is directed to a semiconductor device that solves some or all of the aforementioned problems and a method for making same.